1. Field of the Invention
This invention relates to an optical wiring device, such as an optical connector and a waveguide cable, for optically connecting electronic equipment, boards in electronic equipment, or apparatuses to each other, its driving method, and so forth.
2. Related Background Art
In recent years, the speed of computers, information processing, and computer environment, including displays and printers, has been increasing. At the same time, problems of signal delay, heat generation and electromagnetic radiation emission noise (EMI) due to the electric wiring occur in connections between boards in electronic equipment, between a board and a built-in device, and between electronic equipment. Solutions of those problems are, however, difficult. It is hence apparent that limitations in the electric wiring will be a serious problem in the near future.
Between apparatuses, a system has been developed in which fast transmission by giga-bit Ethernet and IEEE1394 is established by using twisted pair cables or the like. As a transmission system for achieving fast transmission, a method of using a low voltage differential signal with a small amplitude (low voltage differential signalling (LVDS)) is generally used. The range of its use is, however, restricted since costs of its interface IC and cable, such as a twinax cable, are high. Further, in its high-speed transmission at about 1 Gbps, impedance matching is required, and its transmission distance is limited to about 10 m.
Parallel connection, which requires no dedicated integrated circuit (IC), is also frequently employed between boards in an apparatus. However, when its total rate exceeds 1 Gbps, problems occur due to the number of pins, connector reliability, space, skew (delay between channels), and the cost and weight of cables.
Furthermore, in either case, the problem of EMI is serious in the electric wiring, and its seriousness increases as the transmission speed becomes faster.
As a method for solving the problems of limitations in the electric wiring, techniques of optical connection are under course of development. In the optical connection, O (optical)/E (electric) and E (electric)/O (optical) converting portions are ordinarily provided in an apparatus, and the optical coupling is conducted by connecting an optical fiber or the like using an optical connector.
FIG. 1 illustrates an example as disclosed in Japanese Patent Application Laid-Open No. 6(1994)-174981. In FIG. 1, an optical active receptacle 1001 with two-dimensionally arrayed E/O and O/E converting portions is fixed to a wiring board 1050, and an optical connector 1060 is inserted into the receptacle. 1001 such that an optical fiber 1061 is optically coupled to the converting portions. It is thereby possible to achieve a large-capacity optical interconnection by using a bundle fiber 1063. In the structure of FIG. 1, there are further provided a driving electronic circuit 1020, an optical connecting portion 1040, an optical coupling portion 1066, and a guide pin 1067.
Such a system eliminates the signal delay due to parasitic capacitance as appears in the electric wiring, signal degradation resulting from an unstable ground, and EMI emitted from the wiring. The system is therefore expected to be the next-generation in wiring techniques. There is, however, the problem that precise implementation of optical connector and optical device is required to reduce optical losses, and hence, its cost increases and the system is difficult to put into practice. Further, when a large number of channels and optical connecting portions are needed to achieve a large-capacity transmission, problems of yield and space occur, and hence, its use in place of the electric wiring is limited. Furthermore, the system is not reliable for frequent loading and unloading, and ordinary handling is not easy. Therefore, the system is not suitable for use in electronic equipment intended for general consumers.
In the above situation, the following method has been proposed by Japanese Patent Application Laid-Open No. 9(1997)-80360. In this method, an optical coupling portion is built in and fixed to a connector, and a wiring board and an optical wiring cable are connected by the electric wiring. As illustrated in FIG. 2, an optical multi-chip-module (MCM) 1101 with integrated organic waveguide and optical modulator 1107 is fixedly coupled to an optical fiber 1100, and a modulating signal for the optical modulator 1107 is input therein through a pin 1102 for electric connection. Accordingly, when the connector with integrated pin 1102, optical MCM 1101 and optical fiber 1100 is inserted into a conventional socket 1103, the optical connection is accomplished. In the system, the connecting portion need not be precisely fabricated due to its fixed-type optical connection. Thus, cost can be reduced, loading and unloading are easy, reliability is high, and general consumers can handle the optical connector, and hence, a general-purpose connector can be achieved. In the system of FIG. 2, there are further provided an optical coupler 1105, a laser diode 1106 (continuous wave (CW) oscillation), a photodiode 1108, an amplifier 1109, and a Si substrate 1110.
In the system of FIG. 2, however, yield is likely to decrease and there is a limitation to a compact size, because a plurality of high-performance devices (i.e., optical modulators 1107) are arranged on the optical MCM 1101. Further, output light from the laser diode 1106 is branched, so the light intensity is considerably decreased in the case of multi-channel. Furthermore, the module 1101 is constructed by using a plane waveguide. Accordingly, arraying is basically one-dimensional, and hence, the optical cable is likely to be widened when the optical connection is conducted by using a bundle optical fiber or sheet-shaped multi-core waveguide. Thus, the size of the structure increases, and bending handling is restricted.